The hard reset button manually disrupts the power connection with the battery on the power meter housing. The zero offset will not be affected by a hard reset.

To perform a hard reset on the Gen 3. Stages Indoor Power Meter (971-0103): Push the hard reset button, located at the end of the power meter housing. Upon hard reset, the power meter will reboot and resume broadcast.

Note: If your power meter looks like the following image (971-0100 and 971-0101), it will not have a hard reset button.
Please see the related article: How to Hard Reset the Stages Power Meter.